INDOOR RADON DISTRIBUTION IN CLARK COUNTY, WASHINGTON

This study analyzes the distribution of radon throughout Clark County, Washington and shows how that distribution corresponds to the local geology. Radon gas is a naturally occurring geohazard and the leading cause of lung cancer deaths among non-smokers. 3,525 short term radon tests conducted throughout Clark County between 1986 and 2013 have been sorted by the 19 zip codes of the county. Radon risk potential has been mapped by zip code according to the rank sums of maximum radon values, mean radon values, and percentage of tests with radon values >4.0 pCi/l. 15 zip codes show moderate risk potential while 4 show high potential. Not a single zip code was classified as low potential. The maximum values in particular draw the risk levels up, as 18 zip codes show high potential maxima, meaning that a moderate radon risk implies a thin scattering of high values. A more specific look at the rank sum values shows that the greatest concentration of high risk occurs along the Columbia River in Vancouver, in an area aligning with the Mill Plain Pendant Bar. This bar was formed by the Missoula Floods, which deposited highly permeable gravel soils containing some granitic sediments, which have been associated with high radon levels in Oregon. Less permeable flood deposits are seen to the north of Vancouver, which are associated with moderate risk potentials. Other high risk areas, such as Amboy, western Vancouver, and Washougal, are linked to stream deposits of alluvium from reworked Missoula Flood deposits. Despite its danger and prevalence, procedures exist to mitigate hazardous levels of radon gas. It is recommended that all homes in Clark County be tested to determine radon levels. The zip codes with the high potential are: 98660, 98663, 98664 and 98601. One in every five houses has a high radon level (> 4 pCi/l) and the highest indoor value recorded was 61 pCi/l.